Bump helm chart versions post 2.8 release

Change-Id: Iacded169e9193dce471ca2099fd1dc817e6bf58b
diff --git a/VERSION b/VERSION
index 834f262..ffd8a2b 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-2.8.0
+2.9.0-dev